1. Field of the Invention
The present invention relates to a signal processing method, more specifically, relates to a signal processing method for filtering a data obtained by measuring surface texture of an object to be measured such as roughness or a contour etc. of the object to be measured.
2. Description of Related Art
Measuring instruments for measuring surface texture of an object to be measured e.g. contour, roughness, waviness, etc. of a surface of the object to be measured such as a coordinate measuring machine for measuring a three-dimensional shape of the object to be measured, a form measuring machine or an image measuring machine for measuring a two-dimensional contour, a roundness measuring machine for measuring roundness, and further, a surface roughness tester for measuring waviness and roughness etc. of the surface of the object to be measured have been conventionally known. In such measuring instruments a contact type or non-contact type sensor and the object to be measured are moved relatively, to collect measurement data of the surface of the object to be measured.
Usually, disturbances such as noise are contained in thus collected measurement data.
Since the disturbance is usually an electric and magnetic induction noise etc. containing high-frequency components, when the contour of the surface of the object is to be measured, the surface roughness and the waviness can be the disturbance of the contour.
In order to remove the disturbance as necessary, the measurement data is often filtered to remove, for example, the high-frequency components. A spline filter is known as such a filter (refer to Document 1: Japanese Patent Laid-Open Publication No. HEI 9-179992, and Document 2: Japanese Patent Laid-Open Publication No. HEI 8-278343). Further, a robust spline filter is known for applying weight on each measurement data and for repeating to update of the weight until this weighting is optimized.
However, the robust spline filter has been applicable to curve data, but it has not been applicable to curved surface data obtained by measuring a surface area.